There is little motivation right now for vaccination against plague because:
Human infections with plague are fairly rare. A vaccine administered to the general populace would have to be very cheap and extremely safe to make it cost-effective and have a net benefit given the risks of plague are so low, and because
Antibiotics are effective against plague - this makes the likelihood of a widespread outbreak fairly low. Antibiotic resistance could be a concern, but plague would not be one of the most concerning pathogens from that perspective - there isn't much exposure to antibiotics in the reservoir species that the bacterium lives in, so there is less selective pressure towards resistance compared to other bacterial pathogens.
Additionally, plague lives in reservoir species, so extensive human vaccination is not a plausible way to eradicate the bacteria entirely, unlike pathogens that have humans as a primary host.
That said, vaccines are available and can be used for certain individuals at high risk. However, they take a long time to show immune protection (>1 month) making them not that useful during outbreaks. From the same WHO report linked above:
Worldwide, live attenuated and formalin-killed Y. pestis vaccines are
variously available for human use. The vaccines are variably immunogenic
and moderately to highly reactogenic. They do not protect against primary
pneumonic plague. In general, vaccinating communities against epizootic
and enzootic exposures is not feasible; further, vaccination is of little use
during human plague outbreaks, since a month or more is required to
develop a protective immune response. The vaccine is indicated for
persons whose work routinely brings them into close contact with Y. pestis,
such as laboratory technicians in plague reference and research laboratories
and persons studying infected rodent colonies (23).
WHO plague manual: